1. Field of the Invention
The present invention relates to a fluid bearing apparatus, a spindle motor, and a disk drive apparatus.
2. Description of the Related Art
Spindle motors arranged to rotate disks are typically installed in hard disk apparatuses and optical disk apparatuses. Such a spindle motor includes a stationary portion fixed to a housing of the apparatus, and a rotating portion arranged to rotate while supporting the disk(s). The spindle motor is arranged to produce a torque by magnetic flux generated between a stator and a magnet, whereby the rotating portion is caused to rotate with respect to the stationary portion. The stationary portion and the rotating portion of the spindle motor are joined to each other through a fluid bearing. A known spindle motor including a fluid bearing is described, for example, in JP-A 2010-131732. The spindle motor described in JP-A 2010-131732 includes a dynamic pressure bearing including a lubricating oil.
In a fluid bearing of this type, dynamic pressure grooves are sometimes defined by a cutting process. If the dynamic pressure grooves are defined by the cutting process, cut marks in the shape of grooves due to a cutting tool are defined in each of the dynamic pressure grooves. In the dynamic pressure bearing described in JP-A 2010-131732, line grooves, which are cut marks due to a cutting tool, are defined along a circumferential direction.
Once a rotating portion starts rotating with respect to a stationary portion in the fluid bearing, a fluid moves in each dynamic pressure groove obliquely with respect to the circumferential direction, moving from a low dynamic pressure area to a high dynamic pressure area along the dynamic pressure groove. Accordingly, in the dynamic pressure bearing described in JP-A 2010-131732, recesses and projections which define the line grooves extending in the circumferential direction hinder an axial movement of the fluid, which may make it difficult to improve a force of dynamic pressure.